Method of refining lubricating oils



H. L.. ELLENDER METHOD OF REFINING ALUBRIQATING OILS Filed Nov. 15, 1945 Oct. l2, 1948.

" purpose.

Patented Oct. 12, 1948 METHOD OF REFININ G LUBRICATING OILS Harold L. Ellender, Baytown, Tex., assigner to Standard Gil Development Company, a corporation of Delaware Application November 15, 1945, Serial No. 628,819

4 Claims.

This invention relates to an improved method of refining lubricating oils. Particularly, it relates to a solvent extraction process whereby the organic acid content of lubricating oils may be electively reduced. n

Lubricating oil distillates derived from naphthenic and mixed rbase crude petroleum oils frequently contain appreciable quantities of naturally occurring organic acids. These organic acids, such as naphthenic acids, even if present in a lubricating oil in relatively small concentrations, are corrosive to engine parts at the high temperatures to which such oil is usually subjected. It is important, therefore, that motor lubricants not only have satisfactory viscosity index, color, pour and stability characteristics, but also contain organic acids in concentrations insuilicient to cause corrosion difficulties under severe temperature conditions.

In present commercial practice, it is customary to improve the viscosity index characteristics of untreated lubricating oil distillates by treatment in the liquid phase with a solvent that has a preferential selectivity for the low viscosity index y naphthenic-type (relatively less paralnic-type) compounds as compared with the high viscosity index (relatively more paraftlnic-type) compounds. Phenol, furfural, aniline, nitrobenzene and the like are typical solvents used for this Solvents, such as phenol, that do not react with organic acids also demonstrate a preferential selectivity for organic acids of the type usually found in lubricating oil distillates derived from naphthenic or mixed base crudes. In a solvent treating process, therefore, the organic acids tend to be separated from the parai'linic constituents. It has been observed, however, that lubricating oil distillates containing relatively high concentrations of organic acids may be treated with a selective solvent to produce a iinished lubricating oil having satisfactory viscosity index characteristics and yet retaining sufficient organic acids to renderthe solvent treated oil corrosive to engine parts.

In order to effect a substantially complete removal of the organic acids from the high viscosity index paralinic constituents, it is frequently necessary to increase the severity of the solvent treat, that is, increase the ratio of solvent to lubricating oil, above the normal required to produce an oil of desired viscosity index. Increasing the solvent treat decreases the yield of finished lubricating oil obtained in the treating process. In addition, if the solvent treating equipment is operated at its maximum capacity, an increase in the solvent treat above normal necessitates decreasing the amount of oil feed which may be introduced. Increasing the severity of the solvent treat also is disadvantageous in that natural inhibitors present in certain types of lubricating oil distillates and known to be beneficial to motor lubricants are removed from the nished lubricant.

An alternative method of reducing the organic acid content of motor lubricants is that of treating a topped crude or lubricating oil distillate with an alkaline material. For example, it is Well known to the art to remove organic acids present in petroleum oil fractions by distilling a reduced crude in the presence of caustic or other alkaline materials. Th1s procedure has certain disadvantages in that salts of the organic acids and extraneous alkaline material remain in the distillate residue. If the amount of the alkaline materials remaining in the residue is relatively high, the residue may be unsatisfactory for asphalt manufacture or for use as a fuel oil.

In accordance with the present invention, the above disadvantages are eliminated or minimized by removing only a portion of the organic acids present in the lubricating oil distillate with an alkaline material, such as an alkli or an alkali earth metal hydroxide, and subsequently removing essentially all of the remaining organic acids in said distillate by treatment With a selective solvent of the type already mentioned above. In one modification of my invention, a crude oil is charged to a, pipe still or other suitable distilling means to remove gas oil and lower boiling constituents. The resulting topped crude is admixed with a carefully controlled amount of strong, alkali metal hydroxide solution by means of a suitable mixing or contacting device. The mixture of oil and caustic is passed through heating coils or other Suitable heating devices wherein the oil is heated to a temperature substantially that required for subsquent distillation of the oil at subatmospheric pressure. The digested and heated mixture is subjected to distillation at subatmospheric pressure conditions to produce lubricating oil fractions having specified viscosity and flash characteristics and containing the specied amounts of organic acids. The lubricating oil distillate is then treated with a selective solvent in a suitable liquid-liquid extraction process employing conditions such that a iinished lubricating oil essentially free of organic acids and having the desired viscosity index characteristics is y produced.

Experience has shown that motor lubricants derived from mixed base and naphthenic crueles agences should contain organic acids in amounts below, i. e. have a neutralization value below, an equivalent of 0.1 milligram KOH per gram of oil to render said lubricant non-corrosive to engine parts. Experience also has shown that the liquid phase extraction of lubricant distillates containing organic acids in amounts below an equivalent of one milligram KOH per gram of Isaid distillate with a solvent, such as phenol, produces a iinished lubricant having a high viscosity index and contai ing non-corrosive amounts of organic acids. It has been found, however, that lubricant distillates containing organic acids in amounts essentially above an equivalent of one milligram KOH per gram of said distillate require solvent extracting to a lower yield of finished lubricant having a higher viscosity index than is normally required in order to reduce the organic acid content of said lubricant to non-corrosive amounts. Such a motor lubricant -is said to be over extracted; that is, one requirement imposed on the finished lubricant -is met at the expense of other requirements imposed thereon.

One object of my invention is to provide an improved process for refining mineral lubricating oils. Another object of my invention is to provide an economical process wherein maximum yields of solvent extracted lubricating oils meeting both viscosity index and organic-acid-content requirements may be .produced from suitable mineral oils. A further object of my invention is to provide a selective solvent extraction process in which maximum quantities of oil and minimum quantities of solvent are circulated to produce lubricating oils of desired high viscosityindex and low organic acid content without over-extracting the oils, Still other objects and advantages will be apparent to workers skilled in the art to which the -invention relates.

In essence, my invention embodies a process wherein a -crude mineral oil, a reduced crude mineral oil or a lubricating oil distillate is treated with 1an alkaline reagent and then distilled, preferably under non-cracking conditions, while controlling the amount of alkaline reagent introduced into the treating stage` so that a lubricatingoil'distillate having a neutralization value no greater than 1.0 milligram of KOH per gram of distillate is produced from the distillation zone; the distillate having low neutralization value is then extracted with a selective solvent which is non-reactive with the organic acids remaining in the distillate to form extract and ranate phases from the latter of which phases a finished lubrication oil is recovered.

Theinvention will be better understood by reference vto the single ligure which is a diagrammatic flow plan of 'one embodiment of the process. vAcr-ude petroleum oil, or a'distillate or residuum from which gas oil and lighter constituents have been removed in a suitable distillation zone v(not shown), is `conducted through line :'II and pump I2 and is brought into intimate contact with a strong alkaline reagent by a suitable mixing means I3. The alkaline reagent employed may be a 30 to 50 B. aqueous solution of sodi- -um hydroxide. Alternatively, any other alkaline reagents, suchas potassium hydroxide or hydroxides of the alkali earth metals, which react to form stable salts of the organic acids in petroleum may be employed. The alkaline material is obtained from receptacle I4 and is conducted through injection-means I 5 and-line I6 to said mixing means I13. The mixture of alkaline 4material and topped crude is introduced through line I'I to heating coils I8 wherein the mixture is heated in furnace I9 to a temperature essentially that required ln the subsequent subatmospheric distillation process. The heated mixture leaving coils I8 is introduced, by means of line 20 and valve 2I, into distillation column 22. The pressure in distillation column `22 is maintained at subatmospheric conditions by a suitable means (notsshown) in order to minimize degradation of the lubricating oil constituents during the distillation process. The mixture of oil and alkaline material is ashed into distillation column 22 where the vapors therefrom are subjected to fractionation and partial condensation and are separated into fractions having the desired flash and viscosity characteristics and containing a controlled amount of organic acids. The fractions are withdrawn from said column as side streams such as 23, 24, 25 and 26. The amount of alkaline reagent introduced through line I5 is controlled so that the lubricating oil fraction which is subsequently to be processed by solvent extraction, as will be described below, shall have a neutralization value not exceeding approximately 1.0 milligram of KOH per gram of oil.

The degree of condensation in said distillation process may be controlled by the introduction of reflux through line 21 and nozzle 28 in the top of said distillation column. Water, gaseous materials formed during the distillation, and gas oil constituents remaining in the topped crude are withdrawn through line 29 from the top of column 22. The residual material containing heaty lubricating oil fractions, asphaltic con- I stituents, sodium salts of the organic acids and extraneous alkali are withdrawn from the bottom of the column through line 3U.

rEhe condensed lubricating oil distillate to be solvent extracted is withdrawn from one of the afore-mentioned side streams of distillation column 22, for example .line 24, by means of pump 3|., and is conducted through line 32 to a tank or other container I0. From tank I0 said distillate is conducted through line 9 to temperature adjustingmeans 3'3 wherein the distillate is heated or cooled to the temperature desired in the subsequent solvent -treating process. VFrom heating or cooling vmeans 33 the distillate is conducted, by means of line 34, to the lower part of a countercurrent solvent treating ftower 35. A quantity of solventsuicient for treating the distillate to produce a nished lubricating oil having the -desired viscosity index is introduced near the top of solvent treating unit 35 by means of pump 35 and line 37. `To the solvent may be added a small quantity of diluent such as water or alcohol to improve the selectivity of the Vsolvent for the naphthenichydrocarbons and acids. 'Solvent extraction -tower 35 maybe any suitable contacting device to insure intimate contact between .the liquid solvent and the liquid hydrocarbon. Preferably, it is equipped with bell cap plates or Raschig rings. The solvent introduced into the top lof extraction tower 35, by means of line 31, countercurrently contacts 'the hydrocarbon ascending therein. 'The railinate fraction, vcomprising a mixture of paramnic type compounds essentially free of organic 'acids and a Vsmall amount of solvent, is withdrawn from the top of extraction tower 35 by means of line 38. The rafnate leaving 'extractiontower 35 discharges by way of-line 38 into rafnate stripper 40 which is equipped with heating means `4I so that the temperature inzramnate stripper '40 may be adjusted for distillation of solvent from the rafnate. The

solvent distilling overhead from stripper 40'leaves vthrough line 42 and is condensed by a means not shown and may be returned to extraction tower 315 for reuse through pump3'6. Solvent-free raffinate is withdrawn from the bottom of raffinate stripper 40 by means of line 43. The raiiinate is cooled in suitable cooling means 44 before being employed as a motor lubricant.

The solvent extract, comprising the greater portion of the solvent introduced into tower 35,5

naphthenic and aromatic type compounds, and .the grea-ter portion of organic acids contained in Ythe hydrocarbon feed, is withdrawn from the bottom of said tower by means of line 39. Solvent is removed from the solvent extract by means of a; suitable distillation or stripping device (not shown) in conventional manner and solvent may be returned to tower 35 through pump 36 and line 31.

The preferred solvent for use in the presenti;2

invention is phenol or any other selective solvent which does not react with Yorganic acids under conditions existing in the process, and which is preferentially selective for low viscosity index naphthenic-type compounds and for or-.-;

ganic acids.

In the present invention, it will be obvious to those skilled in the art that the critical quantity of caustic introduced into the topped crude prior to the subatmospheric distillation process will de-L.,

acid content of the lubricating oil distillate must* be reduced sufcientl'y to permit obtaining the highest possible yield of solvent extracted lubricating oil meeting viscosity index and acid content requirements. On the other hand, the quantity of caustic or other alkaline material injected into the reduced crude prior to the distillation process should not exceed the amount necessary to meet the above requirements since the value of the residual oil obtained therefrom for asphalt or fuel oil manufacture will be decreased as the quantity of salts and extraneous alkaline material present therein is increased. In general, it has been found in commercial practice that -the neutralization value of lubricating oil distillates should be reduced to about one milligram of KOH per gram of oil prior to solvent extraction in order to obtain high yields of finished lubricants of satisfactory quality.

'Ihe conditions employed in the solvent treating operation vary with the type of solvent em ployed and with the composition of the feed stock charged. In the case of treating distillates derived from Coastal crudes with phenol, oil to solvent ratios in the range from about 1:1.2 to about 1:1.'7, treating temperatures in the range from about 100 to 200 F. and essentially atmospheric pressure are generally satisfactory.

In order to further demonstrate the invention, the following examples are given which should not be construed as limiting the invention whatsoever:

EXAMPLE I In one commercial operation, a topped Coastal crude containing constituents boiling in the lubricating oil boiling range and having no alkaline material added thereto was heatedv in a furnace and distilled at subatmospheric pressure to obtain several lubricating oil distillate side streams. The lubricating oil distillate having a gravity of 21.4

API was countercurrently extracted at a temperature of 165 F. with phenol containing a small lamount of Water. The results of these operations are summarized in the following tables:

TABLE I Material balance [Basis: parts by volume of oil charged] Parts by Parts by Volume volume charged recovered y 0 63 Extract 0 3G Solvent (Mixture of 96 vol. por cont phenol and A vol. por cent water) 155 .TABLE II Quality of oil charge 'and product Charge Raiiinate Gravity API 21.4 25.9 Saybolt Universal viscosity at- 210" F 69.4 59.4 Viscosity Index 22. 7 68 Neutralization Value l# g. KOH/g. oil 1.4 0.08

EXAMPLE n TABLE III Material balance [Basis: 100 parts by volume of oil charged] Parts by Parts by volume volume charged recovered Oil feed 100 0 0 68 0 32 Solvent (Mixture of 96 vol. per cent phenol and 4 vol. per cent water) 130 130 TABLE IV Quality of oil charge and product Rainate Gravity API Saybolt Universal viscosity at- 0 Viscosity Index Neutralization Value Mg. KOH/g. oil

The significant improvement obtained by use of an alkaline pretreatment of the reduced crude before solvent extracting a lubricating oil distillate derived therefrom is illustrated by the higher yield of finished oil obtained and the lower solvent treat required in Example II as compared to Example I. The finished oil obtained in Example II meets all requirements imposed thereon with respect to viscosity index and organic acid content, In Example .1, however, the oil was extracted to a higher viscosity index than necessary in order to lower the acid content of the nished oil to a :satisfactory value. These ldata show, therefore, that by lowering the acid content of this particular lubricating oil distillate by onehalf its original value, the phenol treat may be lowered by 25 volume per cent and the yield of finished oil may be increased by volume per cent to produce a finished lubricating oil of satisfactory quality. This change, therefore, results in an appreciable increase in the oil throughput capacity of a solvent extraction unit.

In another modification of my invention the organic acid content of lubricant distillates may be partially reduced by injecting an alkaline material directly into the distillation equipment employed to separate a crude or reduced crude into its various components. In some cases, it may be desirable to redistill lubricant distillates at reduced pressures over an alkaline medium to effect a reduction of the organic acid contained in the distillate. Another procedure would be that of washing the lubricant distillate With an aqueous solution of caustic or other alkaline material to remove a portion of the acidic constituents contained therein prior to treating said distillate with a selective solvent.

The nature and objects of the present invention having been fully described and illustrated, what I Wish to claim as new and useful and to secure by Letters Patent is:

1. A process for refining mineral lubricating oils having a neutralization value greater than 1.0 milligram of KOH per gram of oil which coniprises intimately contacting a mineral oil comprising lubricating oil fractions and organic acids naturally occurring therein with an alkaline reagent to forni a substantially neutralized minera-l oil, passing the neutralized mineral oil in a stream to a distillation zone and continuously distilling to form a llubricating oil distillate, adjusting the amount of alkaline reagent to obtain a distillate having a neutralization value of about 1.0 milligram of KOH per gram of distillate, extracting said distillate with phenol to form a rainate phase and an extract phase, separately removing the phases and recovering an improved lubricating oil from said raffinate phase.

2. -A process in accordance with claim 1 in which said mineral oil is a lubricating oil fraction obtained by the distillation of crude petroleum under non-cracking conditions.

3. A process in accordance with claim 1 in which said mineral oil is a residuum obtained by the distillation of crude petroleum under noncracking conditions.

4. A process in accordance with claim 1 in which said alkaline reagent is an aqueous solution of an alkali metal hydroxide.

HAROLD L. ELLENDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,081,498 Merrill May 25, 1937 2,154,189 Weir (A) Apr. 11, 1939 2,179,909 Weir (B) Nov. 14, 1939 2,266,359 Edwards et al Dec. 16, 1941 2,295,065 Vesterdal Sept. 8, 1942 2,321,540 Atwood June 8, 1943 2,344,406 Hibshman Mar. 14, 1944 

